GB2114972A - The reaction product of maleic acid or anhydride and pentaerythritol and its use as a secondary stabilizer - Google Patents

Abstract

A secondary stabilizer, mainly intended for vinyl chloride polymers and consisting of a reaction product of maleic acid or maleic anhydride and pentaerythritol. The molar ratio between pentaerythritol and the acid or anhydride respectively of the reaction product is 3-4:1.

Description

SPECIFICATION Improvements in or relating to a secondary stabilizer This invention relates to a secondary stabilizer mainly intended for vinyl chloride polymers.

However, secondary stabilizers in accordance with the invention may also advantageously be used with other similar polymers such as afterchlorinated polyvinyl chlorides, copolymers of vinyl chloride and vinyl acetate, copolymers of vinyl chloride and styrene and others.

Certain vinyl chloride polymers, particularly polyvinyl chloride (PVC), require an addition of stabilizers to prevent decomposition of the polymer at elevated temperatures, for example at the temperatures at which the polymers are worked or processed. Organic stannic compounds are probabiy the best individual stabilizers for this purpose. However, they are rather expensive and they often give unsuitable or unpleasant smells.

Polyvalent metal salts of organic acids are also used as stabilizers for PVC. However, they must be combined with secondary stabilizers to give the same effect as the organic stannic compounds.

Such secondary stabilizers include, for example, organic phosphates, organic sulphur compounds, epoxy compounds and polyhydric alcohols, such as pentaerythritol and trimethylol propane (TMP).

Usually, several of these secondary stabilizers are used at the same time together with the polyvalent metai salts of organic acids. Such combinations of metal salt and secondary stabilizers are mentioned for instance in the United States Patent Specifications Nos. 2,564,646; 2,711,401 and 3,003,999.

The polyhydric alcohols which are available commercially in large quantities are mainly pentaerythritol, TMP and sorbitol and other alcohols based on sugar. Sorbitol and alcohols based on sugar have their greatest use in such connections where the demand for non-toxicity is great, for example in food packages. However, these alcohols suffer from the disadvantage of having a limited thermal stability.

Therefore, a PVC composition containing such an alcohol as a stabilizer may be discoloured when it is subjected to high temperatures during working or processing or later.

Pentaerythritol has a high thermal stability and a high hydroxy equivalent. However, due to its high melting point it has a substantial disadvantage. At the temperature used for working or processing the polyvinyl chloride the pentaerythritol will not meit. Thus, the pentaerythritol will not be dispersed in the plastic material as effectively as those products that are present as a melt at the working temperature of the plastic. As a consequence thereof, the transparency of the finished plastic product is often decreased by the "muddiness" caused by undissolved pentaerythritol particles.

British Patent Specification No. 1,400,91 9 discloses a secondary stabilizer for vinyl chloride polymers. Trimethylol propane and pentaerythritol and optionally one or more of the compounds dipentaerythritol, tripentaerythritol, neopentyl glycol, trimethylol ethane, anhydroennea heptitol and sorbitol are melted together. Then a solid mixture of the compounds used is obtained. The mixture is chilled and finally disintegrated to a powder in the usual way. The secondary stabilizer thus obtained has many good qualities in comparison with previously known stabilizers where different polyvalent alcohols are added separately.

Thus, a much improved compatibility with PVC is obtained as compared with pure pentaerythritol. Furthermore, the stabilizer has a considerably higher melting point than pure TMP. The stabilizer also gives a good transparency of the plastic product produced.

The above difficulties associated with the use of pentaerythritol as a stabilizer for vinyl chloride polymers have been reduced to a great proportion by the process described in British Patent Specification No. 1,400,919.

According to this invention there is provided a secondary stabilizer, suitable for vinyl chloride polymers, consisting of a reaction product of maleic acid or maleic anhydride and pentaerythritol, wherein the molar ratio between pentaerythritol and the acid or the anhydride respectively of the reaction product is 3-4:1.

The preferred secondary stabilizer according to the invention has a lower volatility (sublimation tendency) then the stabilizer described in British Patent Specification No. 1 ,400,9 1 9. Therefore, considerably fewer problems are encountered during the production of plastic products from a plastic material containing a preferred secondary stabilizer in accordance with the invention.

Moreover, generally the preferred stabilizer according to the invention has a higher heat stabilizing effect than the stabilizer described in the said British Patent Specification. Therefore, as a rule, a smaller proportion of stabilizer can be used, which decreased the sublimitation problem further.

Furthermore, the preferred secondary stabilizer in accordance with the invention has a melting point which is lower than the working temperature of the plastic. Therefore, a good transparency of the plastic produced is obtained.

It is very surprising that a secondary stabilizer in accordance with this invention generally gives a better stabilizing effect than the stabilizer described in British Patent Specification No. 1 ,400,9 1 9. The reaction product that constitutes a stabilizer according to the invention contains a considerably lower amount of free hydroxy groups than the polyalcohol mixture described in the said British Patent Specification. Heretofore, the stabilizing effect of a secondary stabilizer has been considered to be proportional to the amount of free hydroxy groups of secondary stabilizer.

The secondary stabilizer can be produced by an esterification reaction only or by a combination of an esterification and an etherification.

In certain cases it can be advantageous to carry out the reaction in the presence of a catalyst.

If a catalyst is used it can be of a type known per se. Strong acids, such as paratoluenesulphonic acid, sulphuric acid etc; metal organic compounds based on tin, zinc or titanium; and Lewis acids, such asBF3 and Al Cl3 are some examples of suitable catalysts. Basic esterification catalysts may also be used.

Depending on the selected method of production the secondary stabilizer will contain ester bonds or ester bonds together with ether bonds.

Like previously proposed secondary stabilizers the present stabilizer is mainly intended to be used together with polyvalent metal salts of organic acids (metal soaps). Often two metal salts are present to complement each other. Examples of such salts are Ca/Zn, Ba/Cd and Ba/Zn.

Either the secondary stabilizer can be charged directly into the PVC-mixture together with the metal soap stabilizer or preblended into the metal soap stabilizer. The blending can be carried out with the components in the form of a powder, or as a solution with a solvent which is then dried off.

The invention will be explained further in connection with the examples given below. Examples 1, 4, 5 and 6 show a production of a secondary stabilizer according to the invention. Examples 2 and 3 comparison examples showing the production of a reaction product between monopentaerythritol and maleic anhydrids in a molar ratio lower and higher respectively than the range specified in claim 1.

These reaction product are unsuitable as a secondary stabilizer. In example 7 it is explained how different secondary stabilizers influence the heat stability of a PVC product at an elevated temperature.

Example 8 shows how different secondary stabilizers influence the discolouration of a PVC product at an elevated temperature. The influence on the light transparency of a PVC product at the use of different secondary stabilizers is mentioned in example 9. In example 10 the tendency of migration out of a PVC product when using different secondary stabilizers is compared.

Example 1 Monopentaerythritol (530.4 9=3.9 moles) was melted with stirring, under a nitrogen gas atmosphere, and at a temperature of about 2600C. Thereafter, maleic anhydride (127.4=1.3 moles) was added in portions during 45 minutes at the same temperature. The mixture was reacted further at the same temperature until 46.7 g H20 (=2.6 moles) had been distilled off. The liquid reaction product was chilled by pouring it on a cold surface. A hard, brittle mass was obtained. The mass was ground to a fine powder. This product is called Product 1 below.

Product 1 had the following qualities: Hydroxyl value 900 mg KOH/g sample Acid value 5.5 mg KOH/g sample Melting point 1 200C (Ball and Ring test) Example 2 Monopentaerythritol (816 g=6 moles) and maleic anhydride (294 9=3 moles) were mixed and heated with stirring under a nitrogen gas atmosphere to a temperature of about 1800 C. The temperature was kept at 1 800C for 1 hour and 25 minutes and then, at the same temperature the pressure was reduced to 20 mm Hg (2,666 N/M2) for 5 minutes). Then 42 g (=2.3 moles) H20 was found to have been distilled off. The heating was then terminated and the transparent liquid reaction product was chilled by pouring it on a cold metal sheet. A tough, sticky product was obtained which could not be ground.The acid value of the product was 14 mg KOH/g sample and the hydroxyl value 910 mg KOH/g sample. The product was wholly unsuitable as a secondary stabilizer.

Example 3 Monopentaerythritol (408 g=3 moles) was melted with stirring under a nitrogen gas atmosphere and at a temperature of about 2500C. Thereafter, maleic anhydride (49 g=0.5 mole) was added in portions during 1 hour at the same temperature. The solution was reacted further with stirring for 2 hours at about 2500 C. Then 18 g (=1 mole) H20 was found to have been distilled off. The heating was then terminated and the transparent liquid reaction produce was chilled by pouring it on a cold metal sheet. A hard, brittle product was obtained. It was ground to a fine powder.

The product had the following properties.

Hydroxyl value 1250 mg KOH/g sample Acid value 2.5 mg KOH/g sample Melting point 1 850C (Ball and Ring Test) Due to its high melting point the product was unsuitable as a secondary stabilizer.

Example 4 Monopentaerythritol (510 g=3.75 moles) and maleic anhydride (245 g=2.5 moles) were mixed and heated with stirring under a nitrogen gas atmosphere to a temperature of about 1 500 C. Then a cloudy solution was obtained. Monopentaerythritol (510 9=3.75 moles) was added at a temperature of about 1 500C by first adding half of it and then after about 10 minutes adding the rest. The temperature was then increased slowly during 1 hour to 2600 C. When 45 ml (2.5 moles) H2O had been distilled off, the product was chilled to 1 800C and the remaining water was distilled off at 1800C and a pressure of 20 mm Hg. (2,666 N/m2. The transparent liquid reaction product was chilled by pouring it on a cold metal sheet. A hard, brittle product was obtained. It was ground to a fine powder.

The product is called Product 2 below.

Product 2 had the following properties.

Hydroxyl 1030 mg KOH/g sample Acid value 5.4 mg KOH/g sample Melting point 1 520C (Ball and Ring Test) Example 7 Monopentaerythritol (544 g=4 moles) was melted with stirring, under a nitrogen gas atmosphere, and at a temperature of about 2600 C. Thereafter, maleic anhydride (98 g=1 mole) was added in portions during 60 minutes at the same temperature. The mixture was reacted further at the same temperature until 43.6 g H2O (=2.4 moles) had been distilled off. The liquid reaction product was chilled by pouring it on a cold surface. A hard, brittle mass was obtained. The mass was ground to a fine powder. This product is called Product 3 below.

Product 3 had the following qualities: Hydroxyl value 994 mg KOH/g sample Saponification value 1 86 mg KOH/g sample Acid value 4.1 mg KOH/g sample Melting point 1 340C (Ball and Ring test) Example 6 Monopentaerythritol (816 g=6 moles) was melted with stirring under & nitrogen gas atmosphere and at a temperature of about 2500C. Maleic acid (174 9=1.5 moles) was then added in portions during 2 hours at the same temperature. The solution was reacted further with stirring for 1 hour at about 2500C. Then 90 g (=5 moles) H2O had been distilled off. The heating was topped and the transparent liquid reaction product was chilled by pouring it on a cold metal sheet. A hard, brittle product was obtained. It was ground to a fine powder. This product is called Product 4 below.

Product 4 had the following properties.

Hydroxyl value 1010 mg KOH/g sample Acid Value 3.0 mg KOH/g sample Melting point 1 280C (Ball and Ring Test) Saponification value 164 mg KOH/g sample Example 7 Eight experiments, hereinafter referred to as experiments 1 to 8 respectively were carried out in a double jacketed mixing vessel provided with a propeller stirrer at the bottom and a double wing propeller above said first propeller.At the beginning of each experiment the mixing vessel was charged with 2000 g PVC (Pevikon S-602 from Kema Nobel AB), 200 g impact strength additive (Kane ACE B28 from Kaneka N.V.), 40 g working assisting agent (K 120 N from Rohm s Haas AB), 12 g inner lubricant (VP6 576 from Henkel s Cie GmbH), 8 g montan wa(Vax OP from Farbwerke Hoechst), 2 g antioxidant (butylated hydroxytoluene), 30 g epoxidized soya bean oil (Edenol D 81 from Henkel s Cie GmbH), 1 0 g calcium stearate (from Swedstab AB) and 10 g zinc stearate (from Swedstab AB).

In experiment 1 no further addition was made. In experiment 2, 10 g fine ground monopentaerythritol (from Perstorp AB) was added. In experiment 3, 10 g trimethylol propane was added and at experiment 4, 10 g sorbitol was added.

In experiments 5-8, 10 g of the products described in examples 1, 4, 5 and 6 respectively above were used.

After the appropriate materials had all been changed into the mixing vessel, in each case heating of the mixing vessel was started by introducing warm water into the jacket. At the same time stirring was started. When the material in the mixer had attained a temperature of 1 1 OOC, the cooling water was fed into the jacket. When the temperature had decreased to 400 C, stirring was interrupted and the vessel was emptied.

At the end of each experiment 1 50 g of the mixture obtained as described above was charged between the rolls of a conventional laboratory two-roll mill having a roll diameter of 1 60 mm. The milling was carried out at 22 rounds per minute. The rolls were heated by steam. The milling temperature was maintained at 170+3 C. A gelatinizing was obtained after 15-25 seconds. Then the object was milled for 5 minutes after the gelatinizing. The thickness of the resultant foil was adjusted to about 1 mm.

The thermal stability of the different foil specimens was measured by introducing a number of samples with a size of 2x2 cm, well packed in an aluminium foil, into an oven having a temperature of 1 800C. The oven had a very good air circulation. Therefore, the temperature could be kept constantly at 1 800 C. The discolouration of the samples was regarded as a measure of the thermal stability. Every fifth minute a complete set of samples was removed from the oven. The time lapsed until a blacking of the samples was obtained is regarded below as the thermal stability expressed in minutes. In Table 1 the results obtained by following this procedure are shown.

Table 1 Thermal stability Experiment no. Polyhydric alcohol in minutes 1 None 25 2 Pentaerythritol 50 3 Trimethylol propane 30 4 Sorbitol 70 5 Product 1 65 6 Product 2 60 7 Product 3 60 8 Product 4 60 The table shows that the products according to the invention give a better stability as compared to conventional polyhydric alcohols. Sorbitol is an exception, but it gives the foil a very strong yellow colour.

Example 8 Eight foils, each about 1 mm thick, were produced exactly in the same way as described in Example 7.

Owing to the different effectiveness of the secondary stabilizers used, foils having a varying degree of discolouration were obtained after this treatment. The discolouration of the foil specimens as a result of the milling process was judged when the foils had been cooled. The following scale of discolouration was used, where 1 relates to the least discolouration and 10 relates to the worst discolouration.

Colour Colour scale 1 yellow-white 2 yellowish 3 weakly yellow 4 yellow 5 yellow-orange 6 weakly orange 7 orange 8 orange-brown 9 brown 10 black In Table 2 below the results of the judging discolouration are shown.

Table 2 Experiment no. Secondary stabilizer Discolouration 1 None 2 Pentaerythritol 1 3 Trimethylol propane 1 4 Sorbitol 5 Product 1 1-2 6 Product 2 1 7 Product 3 2 8 Product 4 2 The table shows that the products according to the invention give a minimal discolouration of the foil. Pentaerythritol is a special case, since it has other disadvantages (see above and examples 9 and 10). Trimethylol propane also is a special case. Its drawbacks are evident from example 7.

Example 9 Eight foils were produced using the same general procedure as in example 7, but the following compounds were the initial components of the mixture, instead of those described in Example 10.

Pevikon S 602 2000 g (Kema Nobel AB) Octyltin stabilizer 0T0-1 5 40 g (Swedstab AB) Glycerol monostearate, Loxiol G 12 20 g (Henkel s Cie GmbH) An octyline stabilized recipe was used, since the effect of the different secondary stabilizers on the transparency of the foil was to be studied in this example. The octylin stabilizer gives considerably less haze in the foil than the combination of calcium stearate and zinc stearate used in the preceding examples.

To eliminate the disturbing influence of irregularities in the surface, the foils were first pressed between glossy plates in a laminate press. The press time was 10 minutes, the moulding pressure- 100 kg/cm2 and the moulding temperature 1 800 C. By the distance plates a foil thickness of 1.0 mm was obtained.

The pressed foil specimens were taken out for measurement of their transparency according to ASTM D 1003-61. In this method, the haze of the specimen is used as a measure of the transparency. In said method the percentage of the entering light, which changes its direction by spreading during passage of the light through the specimen, is measured.

The results of the measurements are given in Table 3 below.

Table 3 Secondary stabilizer Haze, % None 10 Pentaerythritol, 1% 1 7 Trimethylol propane, 1% 1 0 Sorbitol, 1% 12 Product 1,1% 10 Product 2,1 % 10 Product 3,1 1% 11 Product 4,1 % 11 Example 10 The production of eight mixtures was carried out using the same general procedure as in Example 8. However, the following compounds were used in the mixtures, instead of those described in Example 7.

Pevikon S 602, 2000 g (Kema Novel AB) Expoxidized soya bean oil D 81, 100 g (Henkel 8 Cie GmbH) Calcium stearate, 1 5 g (Swedstab AB) Zinc stearate, 5 g (Swedstab AB) Secondary stabilizer, 20 g The sublimitation tendency of the mixtures was measured in the following way: 200 g of the mixture were charged between the rolls of a conventional laboratory two-roll mill having a roll diameter of 160 mm. The milling was carried out at 22 rounds per minute. The rolls were heated by steam. The milling temperature was maintained at 1 90+30C. A gelatinizing was obtained after 15-25 seconds. Then the specimen was milled for 20 minutes after the gelatinizing. The thickness of the resultant foil was adjusted to about 1 mm.Before the start of the milling a beaker having a diameter of 1 90 mm was mounted above the nip between the rolls.

Material from the foil which has migrated out of the plastic material sublimes from the roller nip and condenses on the cold under side of the beaker. After 20 minutes the under side of the beaker was washed with a specified amount of distilled water. The amount of oxygen consuming material in the aqueous solution thus obtained was measured by a simple titration. In Table 4 below the amount of oxygen consumed by the different solutions is shown.

Table 4 Secondary stabilizer mg consumed oxygenllitre None 0.75 Pentaeryth ritol 1.16 Product 1 0.84 Product 4 0.80 Product 3 0.83 Product 4 0.87 The invention is not limited to the embodiments shown, since these can be modified in different way within the scope of the present invention, as defined by the following claims.

Claims (6)

Claims

1. A secondary stabilizer, suitable for vinyl chloride polymers, consisting of a reaction product of maleic acid or maleic anhydride and pentaerythritol wherein the molar ratio between pentaerythritol and the acid or the anhydride respectively of the reaction product is 3 4:1.

2. A secondary stabiliser substantially as herein described in Example 1.

3. A secondary stabilizer substantially as herein described in Example 4.

4. A secondary stabilizer substantially as herein described in Example 5.

5. A secondary stabilizer substantially as herein described in Example 6.

6. Any novel feature or combination of features disclosed herein.